<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport"
        content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Title</title>
</head>
<body>
<script>

  // 原型链： 实例对象与原型之间的连接，叫做原型链
  // 原型链的最外层： Object.prototype
  function Aa() {
    // this.num = 10;
  }

  // Aa.prototype.num = 20;
  Object.prototype.num = 30;
  let a = new Aa();
  console.log(a.num);
</script>
</body>
</html>
